The invention concerns a product containing silicon dioxide and a method for its preparation.
Considerable demand has grown on markets in recent years for fibres which are either incombustible or resistant to combustion. Consequently a number of fibres have appeared on the market which are suitable for textiles inhibiting fire. Fibres containing silicon dioxide are outstanding in their fire-resistance, and they are manufactured by various methods including the Enka method in which regenerated silicon dioxide fibres are spun by the dry method from a waterglass solution from which the excess water has been removed prior to regeneration; this method is described in the patent literature in publications DE-2900990, US-4332601 and EP-160232. In other methods silicon dioxide or silicate glass are used as the raw material, but products made by the former method are expensive while those made by the latter method are too fragile.
GB patent 1064271 presents a relatively inexpensive method for the manufacture of a product containing silicon dioxide. In this case the viscose containing an evenly distributed quantity of sodium silicate is spun in an acid spinbath, where the viscose is regenerated into cellulose and the sodium silicate contained in it is precipitated as polysilicic acid, which is a water-containing form of silicon dioxide evenly distributed throughout the cellulose.
The products manufactured by the above method, for example in the form of fibres, have proved to be extremely usable and inexpensive by virtue of the production method, and because of the water bound in them fire resistant in specific conditions. The fibres have been used in a number of applications including particularly nonwovens and upholstery textiles. During applications development a number of shortcomings have been revealed due to which the fibres are not very suitable for clothing textiles or textiles where a very high level of fire resistance is required. In order to obtain a sufficiently high level of fire resistance the proportion of polysilicic acid should be as high as possible, but for technical reasons it cannot be raised much above 40 percent. One severe disadvantage in textiles which are likely to be washed frequently is that polysilicic acid has a low tolerance of alkaline conditions. It has been observed that using ordinary washing agents the content of polysilicic acid falls to about half the original after only 20 washing cycles. Even a fall of 1 to 2 percentage points in the polysilicic acid content leads to substantially greater combustibility. The high solubility of polysilicic acid in alkalis has also led to problems in dyeing.